Escalators are well known machines for transporting pedestrians and their luggage from one level to another. However, the conventional design is suitable only for straight runs, viewed in plan, which severely limits their possible range of applications.
Moreover 50% of their steps at any one time are wastefully out of use because they are returning underneath the steps which are in use. This also means that a large part of the equipment is below the track so that maintenance may be difficult and expensive.
WO 91/06501 discloses a circular escalator which follows a closed loop having curved and straight sections. The treads of the escalator steps are tapered towards the inner radius of the curve to enable the steps to negotiate the curve. A complicated gearing mechanism causes parts of the inner ends of the steps to splay outwards in order to negotiate straight sections. However, this results in gaps between the steps, and so the escalator is not suitable for carrying passengers on straight sections. Moreover, the radius of the curved sections must be uniform for the length of the curved section, the radius being determined by the extent of the tapering of the step treads. The disclosed escalator could not therefore be used to negotiate a path which had a plurality of curved sections of different radius.
Other curved escalators are disclosed in various patents or patent applications, but these tend either to have tapered steps as described above (see for example U.S. Pat. No. 5,158,167), thereby leading to dangerous gaps on straight sections, or to employ steps which are shaped to move around constant radius curves, but which cannot be adapted for use on curves having different radii. For example, U.S. Pat. No. 5,544,729 employs a complex formula to calculate the shape of each step, but the resulting steps can only be used for use around one particular curve. A slightly simpler system is disclosed in U.S. Pat. No. 5,165,513, but the shape of the steps used therein would result in gaps between the treads if they were used on any path other than a circular one.
Further escalators with these short-comings are disclosed in U.S. Pat. No. 3,878,931, U.S. Pat. No. 4,809,840, U.S. Pat. No. 4,746,000, and U.S. Pat. No. 4,662,502 and U.S. Pat. No. 4,895,239 and U.S. Pat. No. 4,411,352.